Aromatic polycarbonates obtained from 2,2-bis(4-hydroxyphenyl)propane (hereinafter abbreviated bisphenol A) and a carbonate precursor substance are conventionally known as typical aromatic polycarbonates. Since they have a variety of excellent properties; that is, they are transparent and they are excellent in heat resistance and mechanical properties, and good in dimensional accuracy, they are widely used as engineering plastics. However, in recent years, amid the trend that light weight, thinness, and compactness (downsizing) of machinery, tools, and the like are considered important, there are increased cases in which engineering plastics are used at locations closer to heat sources in optical usage. Consequently, it is demanded that engineering plastics be higher in heat resistance, in addition to improving of optical properties, such as light transmittance.
On the other hand, it is known that aromatic polycarbonates excellent in heat resistance can be obtained by reacting 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (hereinafter abbreviated bisphenol AF) with phosgene or a carbonate precursor substance (Japanese Patent Publication No. 12283/1991). However, aromatic polycarbonates obtained from usual bisphenol AF are poor in heat stability, the molded product is colored yellow and is low in light transmittance, and it cannot be used in a field in which high transparency is required.
As one of usages wherein such a high transparency is required, there is a plastic optical fiber. Plastic optical fiber is high in light transmission loss and thus generally cannot be used for a long distance transmission, but since they are flexible and are easy in end workability, they should be useful for signal transmission lines of automobiles and electronic equipment.
Since the core layer of most conventional plastic optical fiber is made of a polymethyl methacrylate, it has a heat resistance no higher than 100.degree. C., and therefore the conventional plastic optical fibers cannot be used in engine compartments of automobiles or in heat-resistant parts of electronic equipment.
To improve this, particularly when heat resistance is required, plastic optical fiber having a core layer that uses a polycarbonate (having structural formula (A) below) is used, but the heat resistance of optical plastic fiber using this polycarbonate is only 125.degree. to 130.degree. C.
Plastic optical fiber having a core layer that uses a polycarbonate AF (having structural formula (B) below) has also been studied. This polycarbonate has a glass transition temperature as high as 157.degree. C. and is excellent in oxidation resistance. However, according to study made by the present inventors, although commercially available bisphenol AF is used to produce a polycarbonate AF, the resultant product is low in light transmittance and poor in heat stability. Therefore, if this polycarbonate AF is used as a core material to make a plastic optical fiber, the transmission loss becomes high and a plastic optical fiber low in transmission loss could not be obtained. Further, when such plastic optical fiber was kept at high temperatures, a large increase in transmission loss was observed. ##STR1##